if i had sex on july 30th and had a 3 day period on august 9th but this month have no period and have always had a 28 day cycle and have never been one to be late could i be pregnant? i keep cramping and my back hurts but i have no period. and i wasnt even worried about being pregnant because i got my period last month. could i still be pregnant if i havent had sex since july 30th?